Various aircraft draw air from turbine compression systems of one or more engines in order to maintain cabin pressure and to power auxiliary systems. The drawn air from the engine(s) is bleed air. In general, bleed air is compressed air that is drawn from a compressor stage of an engine, which is typically upstream from fuel-burning portions of the engine.
Known aircraft include systems that route bleed air through air conditioning systems to cool sub-systems within the aircraft, as well as internal chambers, such as the cockpit and the cabin. However, utilizing bleed air in relation to air conditioning within an aircraft decreases engine efficiency and aircraft range because energy is expended compressing the air, which is subsequently decompressed and re-cooled when used for air conditioning.
Air cycle machines have been used to provide air conditioning for various commercial and military aircraft. A typical air cycle machine utilizes high temperature, high pressure bleed air extracted from the compressor of a main engine, for example. As noted, however, extraction of bleed air expends energy, which is generated through fuel consumption. In short, a portion of the fuel is used to extract the bleed air, which, in turn, reduces the operating range of an aircraft. Further, aircraft range is typically further reduced because a typical air cycle machine has a low coefficient of performance (COP), which may be further reduced as the speed of the aircraft increases.